Motor nameplate data

[thinker]

Motor conductors selection is typically based on the nameplate current (FLA). However, the Standard MG1 allows motor manufacturer a deviation of 10% from the rated value.
Does this constitute a requirement to factor these additional 10% when selecting a conductor size?

 

[rbalex]

Actually motor conductors are NOT selected based on nameplate data in the US; they are selected based on Table values in the NEC. See Section 430.6 of the NEC (2005 Edition)

 

[thinker]

Sorry for not mentioning that in the original post, but this is a special inverter duty motor with not standard voltage and frequency, thus the motor supplier provided nameplate frequency, voltage and current at the base speed.
In this case NEC tables do not apply.

 

[aolalde]

The National Electric Code Art 430 requests: “ were the current rating of a motor is used to determine the ampacity of conductors or ampere ratings of switches , branch-circuit short-circuit and ground fault protection, etc, the values given in tables 430-147 to 430-150 including notes , shall be used instead of the actual current rating marked on the motor nameplate”

 

[thinker]

Aolalde,
In this specific case (VFD driven motor) the Article 430.6(C)applies, which has a reference to nameplate rating. We already confirmed the applicability of this article with local Authority Having Jurisdiction. My question actually was about additional 10% of current. Seems that MG1 allows for that, but NEC does not address this factor.

 

[rbalex]

In this case, what applies is Part X; beginning in Section 430.120.

 

[rbalex]

Section 430.6(C) applies to adjustable VOLTAGE, not frequency.

 

[petronila]

Hello Thinker,

"Motor conductors selection is typically based on the nameplate current (FLA)" Yes,if you use the wire manufacturer tables and derrating factors(room temperature and number of wires in duct) you most have to take account too the leads number and motor connection.For practical matters The FLA could be oversized by 10%.

For the inverter rated motors, use the motor´s current at 60 Hz.The most commun motor´s wires manufacturer use EPDM ,HYPALON, SILICONE AND GLASS Materials.

This link could help:

http://www.belden.com

Regrads

Petronila

 

[thinker]

Rbalex,

430.6(C) does not mention frequency, but the definition "For motors used used in AC, adjustable voltage, variable torque drive systems" fully applies to VFD configuration, and I repeat, we had no problems to get it confirmed officially.

 

[rbalex]

Part X applies, use it. [Former Principal CMP11 (1996)]

 

[waross]

NEC based on 125% of motor current.
This is enough to cover a 10% deviation.
Can you give us the wording of MG11?
respectfully

 

[thinker]

Waross,

The quote from MG1 (Condensed) : "When operated at rated voltage, rated frequency and rated horsepower output, the input in amperes shall not vary from the nameplate value by more than 10 percent"[MG1-12.47]

 

[waross]

Thanks thinker.
respectfully

 

[dpc]

Regarding the NEMA MG1 requirement on nameplate amperage variation:

I do not believe this statement applies to motor running from a VFD. The "rated voltage, rated frequency" means a sine wave.

NEMA standards for ac motor are based on operation from a sine wave unless specifically stated otherwise. This includes standards for efficiency and power factor.